Radio telegraph system



Feb. 26 1924.

J. B. BRADY RADIO TELEGRAPH SYSIIEM Filed Dec. 28. 1921 3 Sheets-Sheet 1 Feb. f 26 1924.

J. B. BRADY RADIO TELEGRAPH SYSTEM Filed Deo. 28 1921 3' Sheets-Sheet 2 IIL .2g

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Feb. 26 1924.

f J. B. BRADY RADIO TELEGRAPH SYSTEM Filed Dec. 28 1921 5 Sheets-Sheet 5 www Patented Feb. 26, 1924.

UNITED STATES JOHN B. BRADY,

F SOMERSET, MARYLAND, ASSIGNOR' TO MOBKRUM COMPANY, 0F

CHICAGO, ILLINOIS, A CORPORATION 0F MAINE.

RADIO TELEGBAPH SYSTEM.

Application led December 28, 1921. Serial No. 525,298.

To all whom it may concern:

Be it known that I, JOHN B. BRADY, a citizen of the United States, residin at Somerset, countyof Montgomery, and tate of Maryland, have invented a certain new and useful Improvement in Radio Telegraph Systems, of which the following is a specification.

My invention relates broadly to the automatic transmission and reception of radio telegraph si als, and more particularly to a system W erein signals may be transmitted upon the operation of a letter keyboard at the transmitter and received simultaneousl in printed type at the receiver.

The object of my invention is to rovide a system for the control of a radio te egraph transmitter from a manually operated' keyboard resembling'a typewriter keyboard and to provide means at the receiver for setting down received signals in type.

A further object of my invention is to provide an impulse system of radio transmission and reception as distinguished from the present dot and dash vcode systems whereby to render substantially secret the messages transmitted.

A further object of the invention is to provide a transmission System which is readily controlled by an operator unskilled in the art of radio telegraphy and to provide a printer receiver which may be operated by one without knowledge of codes as at resent required;

further object of the invention is to provide means whereby code combinations may be readily changed from time to time whereby to render the system substantially secret and the code practically unbreakable.

The transmission system is adaptable for shore or ship station control and in modified form for the control of aircraft radio transmitters from which an observer can communicate to a shore or ship station by operating the lettered keys of a keyboard while the message appears simultaneously in rinted type at the receiver.

e inventlon will be more clearly understoodl by reference to the 'accompanying drawings and the following specification in which:

Figure 1 is a wiringdiagram of the transmitting a paratus; Fig. 2 is a wiring diagram of t le receiving apparatus; Fig. 3 is a perspective view ot' the automatic trans- HEISSUED mitter and printer receiving equipment; and Fig. 4 is a diagrammatic re resentation of the character of impulse c e employed in this system.

The invention as set forth in the particular embodiment shown in the drawings has been successfully operated between the U. S. Naval Aircraft Radio Laboratory at Anacostia, D. C. and the U. S. Naval Radio Research Laboratory, Bureau of Standards, Washington, D. C., the transmitter being controlled by a keyboard and the characters bein rinted at the receiver at rates of Spee eyond that practicable by manual reception and translation. The system comprises broadly a' transmitting unlt having a source of continuous oscillations which may be an alternator, an arc, or a vacuum tube generator. The oscillations are modulated and controlled by a system of impulse transmission involving the starting and stopping of oscillations in an antenna system in combinations of impulses in accordance with an im ulse code. This impulse control is prefera 1y secured by manual operation of a lettered keyboard, the keys of which are arranged to control the operation of a set of contacts so that the latter are either closed or opened through each of a definite number of successive time intervals for each character to be transmitted. The system may utilize continuous waves, interrupted continuous waves or damped oscillations may be emdployed. The transmitter control is arrange for approximately 31 combinations of impulses com rising the characters to be transmitted. he energy radiated from the antenna system is practically irrecognizable on reception by ear as there is no such order of dots and dashes as at present employed in radio telegraphy, the

radiations heilig modified to extend through one or more of a definite number of successive time intervals for each character transmitted. At the receivereither heterodyne or reglenerative acton is employed according to t e nature of t e waves being received. The ener is reduced to an audible frequency an am lifed through a plurality of stages of t ermionic vacuum tube amplifiers. At the final stage of amplication, a power rela is inter-connec comprising a set of para lel connected tubes having a selectively tuned input circuit, and a relay actuated thereby. The relay 1s adapted to open and close a battery circuit through the armature coils of an automatic teletype printer receiver or other printer receiver utilizing impulse reception.

The teletype equipment employed by Way of example in this system is the invention of Charles L. Krum and Howard L. Krum, of Chicago, Illinois. This teletype apparatus is described in an application filed in the U. S. Patent Office by these inventors December 23, 1919, Serial No. 346,948 and in other pending applications, and some features of the telegraph system employed -in connection with such apparatus are described in H. L. Krum Patents No. 1,286,351 dated December 3, 1918 and No. 1,434,290, dated October 31, 1922. Reference is made to these patents and to the ending applications for the details of tiis equipment. However, a general description is given herein.

At the transmitter a keyboard resembling the keyboard of a typewriter is provided. The individual keys of this keyboard are t formed in key bars pivoted at the rear of the machine casing and arranged to be depressed by finger control. Beneath lthe key levers is arranged a set of five selecting bars arranged to be operated or set by the keys in different combinations. A sixth bar operated by each key controls a. clutch by which a contact operating cam shaft is connected to a motor and so rotated through one revolution for each key depressed. The

cam shaft is provided with a set of successively operating cams which effect and time the operation of a set of contacts, such operation being so controlled by a set of selecting fingers operated by the selector bars, that the circuit controlled by the con tacts is either opened or closed through a definite number, preferably five, of successive definite time intervals for each character transmitted, and each character signal being preceded by a starting interval or impulse. That is to say, the contacts are uniformly operated at the beginning of each signal to form a starting impulse and through the remaining five intervals or units of each signal are either opened or closed to form combinations of impulses representing characters to be transmitted. In the case of a vacuum tube radio transmitter the grid circuit may be opened and closed in accordance wilth the sequence of the closing of the set of contacts. In the case of an arc transmitter a uniwave key may be controlled radiating impulses and suppressing impulses in succession. In the case of an alternator a magnetic amplifier may be controlled to start and suppress the radiated impulses. This operation causes the radiation of impulses of high frequency energy from an antenna system.

At the receiver these impulses are reduced to an audible frequency, amplified and then actuate a power relay to energize the armature magnets of a teletype printer. The printer is controlled by a magnet having two coils which operates an armature moved in one direction by the magnet and in the opposite direction by an adjustable spring. he printer mechanism is carried by a suitable frame, the moving parts of which are operated from a motor through the medium of a start and stop clutch which is initiated in operation by the starting impulse or interval of each signal, A rotating selector actuator driven by the motor and thrown into operation by the clutch is adapted to position a set of selectors in different combinations in accordance with the movement of the armature 0f the controlling magnet, and which in turn is controlled by the combinations of impulses striking the receiving antenna system. The shaft carrying the selector actuator is also provided with a transfer cam which at each rotation transfers the setting of the selectors to a second set of selectors or seekers and restores the first set for the next operation.

The main shaft which carries the selector actuator also carries a combiner wheel, a notched ratchet wheel and a type wheel. The seekers cooperate with the combiner wheel to control a trip lever which in turn effects the engagement of a printing dog or arm with the notches of the ratchet wheel and the latter forces a print roller carrying a' paper strip against the letter of the type wheel corresponding to the setting of the seekers, the latter and the print dog or arm being re-set or restored to normal at the end of each revolution of the main shaft by suitable cams mounted thereon. The combination of impulses striking the antenna system at the receiver thus control the operation of the printer mechanism to secure the impression of the characters represented by the signals upon a paper strip.

Figure 1 of the drawings shows the transmitting system comprising an antenna 1, inductance 3, and ground 2. A vacuum tube oscillator is shown energizing the antenna system. The oscillator comprises a set of t ree vacuum tubes 5, 6 and 7 havin grids 12, 14, and 15 connected in parallel an plates 16, 17 and 18 connected in parallel. The filaments 8, 9 and 10 of the vacuum tubes are parallel connected and energized by battery 11. The plate circuit of the oscillators is completed through the antenna inductancc 3, and source of potential 21 back to the filament side of the tubes. The grid circuit of the oscillator connects through grid leak 20 and coupling inductance 4 back to the filament connection on the oscillator. The grid circuit of the oscillator is broken by relay armature 24 and contact 25 for starting and stopping oscillations in the antenna system in accordance with the impulse code employed by the printer system. The relay armature is operated by windings 26 energized by battery 27. This relay circuit is connected to terminals DE on the teletype apparatus represented at 22. A pair of leads 28 are taken beneath this base to the teletype transmitter contacts 29 and 30. These contacts comprise a set of six circuit closing contacts in parallel which are variably operated to secure the starting and stopping of radiation from the antenna system in accordance with the order or combination of impulses ofthe particular character to be transmitted. The relation of the keyboard control with the operation of these contacts has been described above and it will be sufficient here to state that contact 1 forms the starting impulse of each signal While contacts 2, 3, 4, 5, and 6 are variably operated under the joint control of the cam mechanism driven by motor 100 and the key-actuated selectors so as to either open or close the circuit controlled by the contacts during each of the' five selecting intervals of each signal so that ncorresponding combinations of impulses are transmitted. The motor 100 yis maintained at a speed synchronized with the corresponding motor at the distant radio station. Motor 100 has its speed governed by make-andbreak contact 101 which breaks the motor circuitacross a 1000 ohm shunt 102. The excessive sparking at the governor contacts is absorbed by condenser 103. The power supply for the motor is secured through circuit 104.

Referring to Figure 2 of the drawings the radio receiver comprises an antenna system 31, a primary receiving inductance 32, series condenser 33 and ground 34. Inductively associated with the primary winding 32 is secondary winding 35 tuned by variable condenser 36. This adjustable circuit is connected through grid leak and grid condenser 37 with thermionic vacuum tube 38 having heated filament 39, grid 40, and plate 41. The plate circuit includes coupling coil 42 inductively associated with the secondary inductance 35 and including primary 43 of transformer'44 and high potential battery 46. The primary winding 43 is shunted by condenser 45. The filament 39 is energized by battery 47. The circuit is adjustable for both heterodyne and regenerative reception. The transformer 44 has its secondary winding 52 connected to the input circuit of vacuum tube amplifier 48. The amplifier comprises vacuum tube 48 having filament 49, grid 50, and plate 51 and output circuit 53 and 56. The filament 49 is heated by battery 57. The winding 53 forms the primary for transformer 54, the secondary Winding 55 of which is connected to the input circuit of vacuum tube amplifier 58. The vacuum tube 58 comprises the filament 59 energized by batter 67, id 60 and late 61. The output ciicuit giiicludes rirlfiary winding of transformer 64 and hi 1 otential battery 66. The secondary winding of transformer 64 connects to the input circuit of a power amplifier.

The power amplifier herein described by way of example is the invention of F. W. Dunmore of the United States Bureau of Standards. The power relay comprises vacuum tubes 78 and 79 having their grid elements 80 and 81 parallel connected and their plate elements 82 and 83 parallel connected. The filament 84 and 85 are energized from battery 87. A variable negative bias is placed upon the grids 80 and 81 by adj ustable battery 72. The input circuit across the tubes is selectively tuned by condenser 71. The output circuit of the power 4relay includes armature windings 90 of a mechanical relay and high potentialA battery 86. The output circuit may be selectively tuned to the particular frequency of the received signals by means of circuit 91 which may be connected or disconnected from the output circuit by means of switch 92. The mechanical relay 90 has an armature 93 and cooperating contact 94 connected in circuit with battery 95 and to terminals BC upon the teletype apparatus 22. The terniinalsBC beneath the base of the teletype are connected through conductors 96 to the teletype armature coils 99, each coil having terminals 97 and 98 with windings series connected. These armature coils are mounted below a pivoted armature which in operation sets in motion the printer mechanism heretofore dei scribed to produce as a final result the printed character corresponding to the sequence of received impulses.

Figure 3 illustrates in perspective view the teletype apparatus developed by tbe Morkrum Company and used in the present radio telegraph system. The unit comprises.

base 22 carrying the keyboard transmitter contactsV operated by the cam-shaft mechanism, the driving motor, and inter-connecting gearing for the cam-shaft and the printer mechanism. The printer mechanism is carried by a frame 114 visible through window o-pening 109. The printer includes the type wheel 112 and tape guide mechanism 116. The printed tape 117 is delivered through opening 108. The keyboard comprises operating keys 106 and spacer 107 resembling a typewriter keyboard. The

complete apparatus is inclosed in housing having a message copy support 110.

Figure 4 illustrates the character of the code employed in the present system. The characters are made up of five intervals or units of current or no current secured by the opening and closing of the transmitter circuit. The character A for example comprises two contact closures and three spaces or non-contact closures, making up the intervals 2, 3, 4, and 6 upon operation of the contacts 29 an-d 80, of the transmitter keyboard illustrated in Figure 1. Correspondingly the characters B and (l may be formed by a different order of sequence of the intervals as illustrated in Figure e. The keyboard is provided with a shift key whereby characters may be transmitted on the upper case or the lower case as desired.

The operation of the system has probably been made clear from the specification above but may be repeated here briefly. At the transmitter the grid circuit of a vacuum tube oscillator is uniformly closed during the starting interval of each signal and is thereafter either opened or closed during the five selecting intervals of the signal to radiate from the antenna a starting impulse followed by a combination of impulses corresponding to the character to be transmitted. This is accomplished by depressing a key upon the teletype keyboard causing the operation of the cam-shaft mechanism which under control of the key-actuated selectors, operates the transmitter contacts duringthe starting and selecting intervals of each signal to thereby eifect radiation from the antenna system during each starting interval and thereafter either effect or prevent radiation from the antenna system during the five remaining selecting intervals. At the receiver this energy is reduced to an audible frequency and amplified, and operates the selective power relay to move the teletype armature in the same order of sequence as the radiations are transmitted from t-he distant transmitter.

The armature causes the proper positioning of the type wheel and operation of the print dog to print the proper character by the printer mechanism above described giving the result of a printed character simultaneously with the depression of that same lettered key at the distant transmitter keyboard.

In t-he tests conducted between the United States Naval Aircraft Radio Laboratory, Anacostia. I). C. and the United States Bureau of Standards successful operation was obtained at a speed beyond that practicable by manual operation. and messages were transmitted in clear and concise order.

The system to all practical purposes is substantially secret inasmuch as the signals are not readable by aural reception. The system is capable of substantially secret operation by interchange of type wheels at the receiver with a corresponding change of designating caps upon the keys at the transmitter keyboard.

Having thus described my invention what I claim and desire to secure by Letters Patent is:

1. In a system of radio telegraphy, a

transmitter comprising an electron tube oscillator, a grid control circuit therefore, means for either opening or closing said grid circuit through each of a definite number of successive definite time intervals for each character signal to thereby radiate energy in corresponding combinations of impulses and means for receiving said impulses, means for am lifying said impulses, a relay actuated by said impulses and a ty e printer controlled by said relay where y said impulses select particular characters and cause said characters to be printed.

2. In a system of radio telegraphy, a transmitter comprising an electron tube oscillator for generating continuous oscillations, means for variably modifying the radiation of said oscillations during each of a definite number of successive time intervals for each signa-l to thereby produce a characteristic succession of impulses, means for receiving said impulses, means for amplifying said impulses and a selective relay operated by said impulses and adapted to cont-rol a circuit to an automatic printer having means controlled by said combinations of impulses for selecting characters and causing same to be printed.

3. In a system of radio telegraphy, a transmitter comprising a plurality of electron tubes for generating oscillations, means for controlling the radiation of impulses comprising a keyboard, a set of contacts and means selectively controlled by the keys of said keyboard for either opening or closing said contacts through each of a definite number of successive definite time intervals to produce a characteristically timed succession of impulses for each signal, a receiver, means for receiving and amplifying said impulses` an electron tube relay actuated by said impulses, means for selecting the position wof a type printer wheel in accordance with the series of impulses, and means for printing said character at the receiver in accordance with a character type in accordance with the succession of impulses and means cooperating with said type to print the corresponding character.

4. In a signaling system, the combination at a transmitter of a plurality of electron tubes having grid, filament and plate electrodes for generating oscillations, an oscillating circuit interconnecting said electrodes, an antenna ground system connected to said oscillating circuit, selective means comprising a plurality of keys, a set of i ra'tus for receiving the transmitted signals, an electron tube relay controlled by said apparatus and lhavin grid, filament and plate electrodes, a clrcuit including said plate and a magnet, an armature operated y said magnet in accordance with the succession of impulses of each signal, and means controlled by the operations of the armature in response to each succession of -impulses for selecting and printing the correspondin character.

5. A ra io transmitter comprising in combination an antenna ground system, an elet',- tron tube oscillator for producing high frequency oscillations, a rotating cam shaft.

cooperating contacts and means for seleclv tively controlling the operation of said cam shaft upon said contacts to thereby either e'ect or arrest the radiation of oscillations from said antenna ground system during each of a definite number of successive time intervals or units for each si al.

6. In a signaling system, t e combination -at a transmitter of a plurality of electrony tubes having grid, flament'and plate electrodes for generating oscillations, an oscillating circuit interconnecting said electrodes, an antenna ground system connected to said oscillating circuit, selective means comprising a plurality of keys, a set of contacts and Contact operating means controlled by the movement of each of said keys Whereby said oscillations may be modulated, for each character signal, during eac-h of five successive definite time intervals to produce a characteristically timed succession of impulses; at a receiver, an electron tube apparatus for receiving the transmitted signals, an electron tube relay controlled by said apparatus and having grid, filament and plate electrodes tuned to the tone frequency of the transmitted signals, a circuit including said plate and a magnet, an armature operated thereby in accordance with leach succession of impulses and a power-actuated printing mechanism mechanically an l selectively controlled by each succession ciV operations of said armature for printing a character in accordance with the corresponding succession of impulses.

7. In a system of radio telegraphy, a transmitter comprising a generator of sustained oscillations, means for modifying the radiation of said o-scillations during each of a deiinite number oi successive time intervals to thereby produce a characteristically timed succession ofimpulses for each character signal, means for receiving said impulses, means ior amplifying said impulses, means operated by said impulses and adjusted to correspond to the tone frequency thereof to control a circuit to an automatic printer having means controlled by each succession of impulses for selecting a character and causing same to be printed.

8. In a system of radio telegraphy, the combination at a transmitter of an electron tube oscillator and selectively controlling means therefor arranged to place said oscillator, for each character. signal transmitted, in either one of two conditions during each of a definite number of successive time intervals of definite duration, to thereby pro duce a characteristically timed succession of impulses for each character signal; at a receiver, an electron tube apparatus for receiving and amplifying the transmitted signals, an electron tube relayT responsive to the amplified impulses of the signals, a magnet controlled by said relay, and a printer umechanism selectively controlled by said magnet for printing characters in accordance with the signals.

JOHN B. BRADY. 

